Days after a majority of government MPs voted to maintain the Coalition's position against legalising same-sex marriage, thousands of people gathered in the CBD to take part in the city's biggest marriage equality demonstration yet.

Speaking at the event, Opposition Leader Bill Shorten reiterated his promise that if Labor won the next election, he would introduce a bill to legalise marriage equality within the first 100 days of office.

"This week Mr Abbott and his right-wing Liberals broke the heart of the nation," Mr Shorten said. "They are holding Australia back. It should not be the case that people are treated as a second-class citizen merely because of who they love... Why is Mr Abbott so stuck in the past that he's worried about who someone else marries? Get a life!"

People attending a Marriage Equality rally in Melbourne. Credit:Chris Hopkins

Saturday's rally marks 11 years since the ban on marriage equality was put in place in Australia. But while dozens of rallies have taken place over the years, Tuesday's Coalition party room meeting in Canberra - which killed off the chances of same-sex marriage being legalised this term - has reignited the debate and sparked internal divisions within Liberal ranks.

Instead of allowing a free vote on the issue, the government has opted to put the matter to a public vote after the next federal election.

However, the exact timing and mechanism isn't clear, with some in cabinet pushing for a referendum (which not only requires a majority of people, but also requires a majority of people in a majority of states for change to take place) or a plebiscite.

Equal Love organiser Ali Hogg said it was obvious Mr Abbott was using the plebiscite as a stalling tactic, but added that if a public vote was to take place, it was certain to pass.

Greens MP for Melbourne Adam Bandt said Mr Abbott's actions this week had "signed this government"s death warrant", while Victoria's first commissioner for gender and sexuality, Rowena Allen, told the crowd about her wife and rainbow family, declaring "this is personal for me".

The rally began at the State Library on Swanston Street, with organisers estimating at least 10,000 people took part.

By 2pm, the clouds had disappeared just in time for the crowd to begin marching through the CBD to the Old Treasury Building on Spring Street for a mass "illegal wedding".

Melbourne couple Claire and Steph Eden-McIlroy - both wearing identical hooded jumpers emblazoned with the words "some chicks marry chicks; get over it" - were one of several same-sex couples who took part in the ceremony.

Steph, 25, said they were just like "any other loved-up couple" and wanted to be treated equally under the law.

She said that legalising same-sex marriage "would tell our future generations that they are accepted and valued, to be who they want to be."

Antony McManus and his partner of 28 years, Ron Van Houwelingen, also took part in the mock wedding ceremony – their 10th illegal marriage so far.

Loading

"We were hoping the 10th ceremony would be legal," Mr Van Houwelingen said.

Both men said they were disappointed by this week's events, and questioned Mr Abbott's motivation for a potentially expensive and non-binding public vote.